Frontlit illuminated touch panel

ABSTRACT

A frontlit touch panel for use with a reflective light valve, comprising a front light guide having at least one light input face that supplies light to the guide, a viewing face, a light output face opposite the viewing face, and at least one component of a touch-sensitive transducer, the light output face having a light extraction layer thereon having a substantially flat light exit face and containing buried reflective facets that extract supplied light from the guide through the light exit face. The touch panel can be used with a light source, reflective light valve and suitable control electronics to form a compact, efficient illuminated touch panel display assembly.

TECHNICAL FIELD

This invention relates to touch panels and to electronic displays.

BACKGROUND ART

Flat panel displays are typically backlit by light guide slabs (oftenreferred to as “backlights”) that provide uniform illumination to atransmissive light valve. The backlight may be the primary light sourcefor the display, or a source of supplemental illumination in apredominantly reflective (often referred to as a “transflective”)display. Alternatively, flat panel reflective displays may be front-litby a light guide slab (often referred to as a “frontlight” or “frontlight guide”) that provides uniform illumination from the viewing sideof a reflective light valve. This allows elimination of the backlightand placement of a reflector in the light valve, thereby increasing thedisplay's reflectivity and brightness in well-lit ambient lightconditions when the frontlight is turned off. Front light guides shouldhave sufficient clarity so that they do not distort or significantlyattenuate the display image. Preferably the front light guide alsouniformly illuminates the display at a brightness level sufficient torender the display readable in dark ambient conditions.

Displays may also incorporate touch panels that allow the user to inputinformation via a stylus or finger pressure. For example, a common typeof touch panel known as a “resistive overlay” design utilizes twotransparent layers with partially conductive coatings separated byspacers. When the layers are pressed together, the electrical resistanceis sensed in two dimensions to obtain the coordinates of the contactpoint. The bottom layer (the layer closest to the display) typically isquite stiff and made of glass. The top layer (the layer that will betouched by the stylus or finger) typically is fairly flexible and madeof plastic.

Resistive overlay and other touch panel designs are described in the“Carroll Touch Handbook”, available at www.carrolltouch.com. Many suchother touch panel designs, including “capacitive overlay”, “guidedacoustic wave”, “surface acoustic wave” and “near field imaging” (seeU.S. Pat. No. 5,650,597) touch panels, incorporate an optically clear,relatively stiff slab atop the display. Some types of “scanninginfrared” touch panels also incorporate an optically clear, relativelystiff slab atop the display. As with resistive overlay designs, glass ismost commonly used to form the stiff slab.

Japanese Published Patent application No. JP 11344695A (equivalent to WO9963394) shows an integral front light guide and touch panel in whichthe light guide portion is made of molded plastic. The upper surface ofthe light guide is bonded to the lower surface of the touch panel usinga layer of transparent resin, and the lower surface of the light guidehas a polygonal or circular dot pattern formed by an ink of transparentor semi-transparent resin having a higher refractive index than thelight transmission plate and containing a photodiffusion pigment.Alternatively, the lower surface of the light guide can be formed with“fine crimps” or with “prisms” (shown as sawtooth projections) formedparallel to the end face of the input of the light transmission plate.The light guide of this reference utilizes scattering by theabove-mentioned photodiffusion pigment, or refraction through theabove-mentioned crimps or prisms, to extract light from the light guideinto a light valve. The sawtooth projections in this reference areoriented with the inclined portion of the sawtooth facing away from thelight input end of the light guide.

Japanese Published Patent application No. JP 2000-47178A shows anintegral front light guide and touch panel in which the light guideportion is wedge-shaped and has a pattern of spacers on its uppersurface. The light guide of this reference utilizes scattering by thespacers to extract light from the light guide into a light valve.

Other illuminated touch panel display devices are shown in JapanesePublished Patent Application Nos. JP 61188515A, JP 11065764A, JP11110131A, JP 11174972A, JP 11260133A, JP 11316553A, JP 11065764A and JP2000075293A, and in PCT Published Patent Application No. WO 99/63394A.

U.S. Pat. No. 5,396,350 shows a backlight having an array of microprismsthat reflect light into a transmissive light valve.

U.S. Pat. No. 5,428,468 shows an illumination system employing awaveguide and an array of microprisms that reflect light out of thewaveguide. U.S. Pat. No. 5,995,690 shows a light extraction tape forcoupling light out of a waveguide.

Other illuminated frontlit or backlit illumination or display devicesare shown in U.S. Pat. Nos. 4,373,282; 4,528,617; 4,751,615; 4,799,137;4,811,507; 4,874,228; 5,005,108; 5,050,946; 5,054,885; 5,190,370;5,341,231; 5,359,691; 5,485,354; 5,506,929; 5,555,109; 5,555,329;5,575,549; 5,594,830; 5,608,550; 5,608,837; 5,613,751; 5,668,913;5,671,994; 5,835,661; 5,894,539; 6,011,602 and 6,139,163; and inEuropean Patent Application EP 0 802 446 A1.

SUMMARY OF INVENTION

Typically, touch panel fabrication requires one or more manufacturingsteps that involve high temperatures or other harsh processingconditions. For example, many touch panel designs employ a conductive orcapacitive layer of indium tin oxide (“ITO”). The processingtemperatures required to apply a satisfactory ITO layer will destroymost plastic substrates. The touch panel also should have good opticalproperties. Thus the touch panel often includes a heat-resistant glasssubstrate that can support an ITO layer or other heat-processable layersof the touch panel. Such touch panels can be combined with a separatefront light guide, which should also have good optical properties,including good light extraction characteristics. The front light guidecan be made, for example, from a molded plastic wedge, and the resultingcombination placed atop a reflective light valve. This approach employsextra parts, has an extra interface in the supplied light path, and hasincreased overall thickness. However, such an approach also permits thelower slab of the touch panel to be fabricated from flat glass, which isrelatively low in cost and can survive the processing steps required toform a layer of ITO or other applied material.

Although a number of illuminated touch panel devices have been proposed,there is an ongoing need for thinner, more efficient or more evenlyilluminated devices, for devices that could be more easily constructed,and for devices with reduced power consumption. Many current devices donot use all of the light supplied by the light source. If such unusedlight could be channeled to the display, then power consumption could befurther reduced and display brightness could be increased.

Some of the above-mentioned illuminated touch panel devices employscattering or refraction to extract light from the light guide. Theseapproaches can cause reduction in contrast, or can supply light at lessthan optimal angles to a light valve in the display.

The present invention provides, in one aspect, a frontlit touch panelfor use with a reflective light valve, comprising a front light guidehaving at least one light input face that supplies light to the guide, aviewing face, a light output face opposite the viewing face, and atleast one component of a touch-sensitive transducer, the light outputface having a light extraction layer thereon having a substantially flatlight exit face and containing buried reflective facets that extractsupplied light from the guide through the light exit face. The touchpanel can be easily fabricated, for example, by fabricating a component(e.g., a conductive or capacitive layer) of a touch-sensitive transduceron an ordinary flat glass sheet, and by laminating the resultingassembly to a plastic extraction film. An optional top membrane can beapplied atop the touch panel, and an optional antireflection coating canbe applied to the light exit face of the structured-surface film.

The present invention also provides an illuminated touch panel displaycomprising:

-   -   a) at least one light source;    -   b) a front light guide having at least one light input face        through which light from the source can be supplied to the        guide, a viewing face, a light output face opposite the viewing        face, and at least one component of a touch-sensitive        transducer, the light output face having a light extraction        layer thereon having a substantially flat light exit face and        containing buried reflective facets that extract supplied light        from the guide through the light exit face; and    -   c) a reflective light valve that receives extracted light from        the guide and returns at least some of that light through the        viewing face.

Compared to the use of a separate touch panel and front light guide, thefrontlit touch panels of the invention can have reduced overallthickness, higher transmission and fewer interfaces. The panels can befabricated using ordinary flat glass and existing touch panelmanufacturing methods and equipment to provide a touch panel havingadded functionality. Preferably the frontlit touch panels of theinvention have a composite construction comprising a layer of glass andone or more other layers made of different materials (e.g., conductivelayers, solder traces, sensors or othertouch-sensitive-transducer-related components on one major face of thetouch panel, and a microstructured plastic surface and optionalantireflection coating on the other major face of the touch panel).Preferred embodiments of the panels efficiently extract supplied lightwhile exhibiting good contrast and low distortion. Because the frontlittouch panel has microstructured reflective optics located between thetouch panel and the light valve and because the touch panel can have asmooth viewing face, the frontlit touch panels of the invention arerelatively robust and are less likely to be damaged than touch panelshaving microstructured optical features on the viewing face.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view of an illuminated frontlit touch panel display ofthe invention.

FIG. 2 is a simplified side view of the touch panel of FIG. 1, showingthe general path taken by ambient and supplied light rays.

FIG. 3 is a magnified side view of a portion of the touch panel of FIG.1 and FIG. 2, showing the structured light extraction layer and the pathtaken by a supplied light ray.

FIG. 4 is a magnified side view of a portion of an illuminated frontlittouch panel of the invention having a low ratio of plateau length toland length.

FIG. 5 is a magnified side view of a portion of an illuminated frontlittouch panel of the invention having a high ratio of plateau length toland length.

FIG. 6 is a graph showing the relationship between the ratio of plateaulength to land length and extraction efficiency.

FIG. 7 is a magnified partial side view showing a source of lightleakage.

FIG. 8 is a magnified partial side view showing a source of ghosting.

FIG. 9 is a magnified partial side view showing an extraction structurethat can reduce light leakage and ghosting.

FIG. 10 is a magnified partial side view showing a light guide and anextraction structure that can reduce light leakage.

FIG. 11 is an exploded side view of a touch panel and light guide of theinvention.

FIG. 12 is an exploded side view of another touch panel and light guideof the invention.

DETAILED DESCRIPTION

When terms such as “above”, “atop”, “upper”, “upward”, “beneath”,“below”, “lower” and “downward” are used in this application to describethe location or orientation of components in a display, these terms areused merely for purposes of convenience assuming that the display isviewed with its touch-sensitive surface facing generally upwards. Theseterms are not meant to imply any required orientation for the completeddisplay or for the path taken by supplied or ambient light in actual useof the completed display. Some of the components of this invention andtheir relationship to one another can also conveniently be described bycomparison to a reference plane. For purposes of this invention, thereference plane will be taken to be the plane formed by (or closelyapproximating) the light output face of the front light guide, whichusing the orientation convention described above would be the lower faceof the light guide.

Referring now to FIG. 1, an illuminated touch panel display generallyidentified as 10 is shown in schematic form. Supplied (in other words,non-ambient) light from source 42 will enter coupler 44,where ittypically is converted from a point source or sources to a line sourcesuitable for use in illuminated touch panel display 10. The suppliedlight then enters light input face 14 of front light guide 12, and asexplained in more detail below in FIG. 2 and FIG. 3 passes down into andthen back up out of reflective light valve (in this case a reflectiveLCD) 36. Light guide 12 also has opposing end 15, light output face 16and viewing face 18. An optically transparent adhesive (not shown inFIG. 1) fastens structured light extraction layer 32 to light outputface 16 of light guide 12.

Viewing face 18 and flexible membrane 26 have respective conductivecoatings 20 and 24. Coatings 20 and 24, spacers 28 and flexible membrane26 form a touch-sensitive transducer 23 that can provide an indicationof a command or a position on viewing face 18 when a digit, stylus orother suitable instrument is used to press downward on flexible membrane26. Associated electronics (not shown in FIG. 1) can be used tointerpret the touch location on viewing face 18, and to provideelectronic signals to control or otherwise influence other electronicdevices or components.

Light guide 12 and layer 32 form the remaining portion 21 of illuminatedresistive touch panel/front light guide assembly 22. An air gap 35separates the lower face 33 of layer 32 from polarizer 38, which liesatop reflective LCD 36. Reflective layer 40 is located on the bottom ofreflective LCD 36, and (assuming that reflective LCD 36 is suitablymodulated to permit the passage of light) serves to return light thatpasses from assembly 22 through reflective LCD 36 back towards assembly22.

The illuminated touch panel shown in FIG. 1 employs a resistivetouch-sensitive transducer. Those skilled in the art will appreciatethat other types of touch-sensitive transducers can be used in theinvention. For example, the touch-sensitive transducer can operate via acontact mechanism such as capacitive overlay, guided acoustic wave,surface acoustic wave or near field imaging. The touch-sensitivetransducer can also operate via a non-contact mechanism such as ascanning infrared sensor, e.g., via provision of a suitable array oflight beams and photosensors above or below the upper face of the lightguide. Those skilled in the art will also appreciate that a variety oftouch-sensitive transducer components can be employed in the presentinvention, and that the touch-sensitive components need not involve aconductive layer made of ITO or other heat-processed material.

Referring now to FIG. 2, light rays such as supplied light ray 45 fromsource 42 are reflected towards the opposite end 15 of light guide 12 bytotal internal reflection off face 18. Upon striking light output face16 at a suitable angle, light ray 45 will pass into structured lightextraction layer 32. If a facet (not shown in FIG. 1 or FIG. 2) of layer32 is struck at a suitable angle by light ray 45, light ray 45 will bereflected from the facet, exit through the lower face 33 of layer 32 andthereby be extracted from light guide 12. The extracted light will passthrough air gap 35, and then enter polarizer 38 and reflective LCD 36.Assuming that reflective LCD 36 is suitably modulated to transmit light,light ray 45 will pass into reflective LCD 36, strike reflector 40, bereflected back through reflective LCD 36 and polarizer 38 into layer 32and light guide 12, and exit light guide 12 through viewing face 18(passing through coatings 20 and 24 and membrane 26), whereupon lightray 45 can be seen by viewer 48.

If the ambient light level is sufficiently high, then informationconveyed by illuminated touch panel display 10 can be seen by viewer 48without the need for illumination by light source 42. Ambient light rayssuch as ambient ray 50 enter illuminated touch panel display 10 throughmembrane 26, pass through the various components and layers mentionedabove, and (assuming that reflective LCD 36 is suitably modulated)strike reflector 40 and are reflected back through reflective LCD 36towards viewer 48.

In illuminated touch panel display 10, supplied light from light source42 is guided between two generally parallel faces 16 and 18 within thelower portion 21 of touch panel assembly 22. The light guide need nothave generally parallel faces. However, because faces 16 and 18 of thelight guide shown in FIG. 1 and FIG. 2 are generally parallel, lightguide 12 can be made from a low cost, durable material such as plateglass. Conductive layers, solder traces or other touch-sensitivetransducer components can be formed on the first major face of lightguide 12. The light extraction layer, optional antireflection coatingand other optional light management features or layers can be formed onthe second major face of light guide 12. Owing to the relatively harshprocessing conditions typically required to form such touch-sensitivetransducer components, the touch-sensitive transducer componentspreferably are completely formed on the first major face of light guide12 prior to formation of the light extraction layer and other optionalfeatures or layers on the second major face of light guide 12.

Referring to FIG. 3, a portion of the illuminated front light touchpanel display of FIG. 1 and FIG. 2 is shown in a magnified side view.Light extraction layer 32 has a light exit face 33 and an upper surfacehaving a plurality of projections such as projections 52 and 53 thatface or point toward (and preferably optically contact) light guide 12.Face 33 is “substantially flat”, that is, face 33 is sufficiently flatto avoid inducing objectionable distortion in display 10. The uppersurface of layer 32 is “structured”, that is, it has a non-planartopography having finely-shaped features (such as projections 52 and 53)that can affect the direction or intensity of light rays that strike theupper surface of layer 32. Projections 52 and 53 are flanked by landportions such as lands 60 a and 60 b, and by enclosed pockets such aspockets 58 a and 58 b containing a medium (e.g., air) having a lowerrefractive index than the material from which layer 32 is manufactured.The projections have riser, plateau and facet portions such as riser 54a, plateau 55 a and facet 56 a. For purposes of discussion, projectionssuch as projections 52 and 53 can be referred to as “generallytrapezoidal”, even though the projections have only three sides and eventhough a quadrilateral formed by drawing an imaginary line to completethe fourth side of a projection might not have two parallel sides.

The plateaus are laminated to light guide 12 using transparent adhesive50. Plateau 55 a lies against adhesive 50 and is generally coplanar withthe other plateaus of layer 32. Facets such as facet 56 a are “buried”in light extraction layer 32, that is, such facets lie within layer 32,between light output face 16 of light guide 12 and light exit face 33 oflayer 32. Riser 54 a adjoins plateau 55 a, which in turn adjoins facet56 a. Preferably (disregarding for the moment any intervening layer oftransparent adhesive), the facets are adjacent to or very near lightoutput face 16 and spaced more remotely from light exit face 33.

Facets such as facet 56 a are oriented so that light from the input faceof light guide 12 such as supplied light ray 46 can pass throughadhesive 50 and plateau 55 a, strike facet 56 a, be reflected downwardsand thereby be extracted from light guide 12 through exit face 33. Thesupplied light is thus extracted from the light guide using reflectiveoptics. Many of the illuminated touch panel assemblies that haveheretofore been proposed employ an extraction mechanism that relies onrefractive optics, for example by employing a prismatic (e.g., sawtooth)surface on the exit face of the light guide.

Supplied light can be extracted from the light guides of the inventionat normal or near-normal angles with respect to the reference plane. Inother words, the supplied light can be extracted at a zero or near-zeroangle of incidence with respect to the light valve. This can provideimproved coupling of extracted light into the light valve compared tolight guides that rely on refractive extraction. Using refractiveextraction, it is difficult to achieve extraction angles whose centroidis greater than about 40° with respect to the reference plane. In otherwords, it is difficult to achieve less than about a 50° angle ofincidence of the centroid of the extracted light with respect to anormal to the light valve. If the extracted light reaches the lightvalve at too high an angle of incidence, then the light valve will notefficiently reflect light toward the viewer, or additional optics (e.g.,additional refractive optics) will be required to redirect the extractedlight.

An extractor based on reflective optics is less sensitive to variationsin wavelength of the supplied light than an extractor based onrefractive optics. This can provide improved color uniformity in theilluminated touch panel displays of the invention compared to someilluminated touch panel displays that have heretofore been proposed.Stray reflections, which can lead to objectionable ghosts and loss ofcontrast, are also less pronounced with reflective extractors comparedto refractive extractors. The stray reflections that do arise inreflective extractors tend to be directed away from the viewer. Inrefractive extractors, some stray reflections tend to be directedtowards the viewer, leading to a loss in overall contrast. If such strayreflections are referred to as noise bands, then their presence alongthe viewing axis represents a source of noise and a loss in signal tonoise ratio.

The use of reflective extraction optics in the illuminated touch panelsof the invention thus can provide improved design flexibility andperformance compared to the use of refractive optics.

Those skilled in the art will appreciate that although lands such aslands 60 a and 60 b are shown in FIG. 3 as being parallel to thereference plane, they need not be parallel. In addition, risers such asriser 54 a need not be symmetrically inclined with respect to thereference plane. Likewise, facets such as facet 56 a need not besymmetrically inclined with respect to the reference plane.

Those skilled in the art will also appreciate that the projections onlight extraction layer 32 can have shapes and orientations other thanthose shown in FIG. 3, so long as proper extraction of light from lightguide 12 into reflective LCD 36 takes place. The angle at which suppliedlight from source 42 enters light guide 12, and the dimensions, pitchand angular orientation of the projections on light extraction layer 32preferably are selected so that supplied light is evenly distributedacross the viewing face of illuminated touch panel display 10.

FIG. 4 through FIG. 6 illustrate the effect of the ratio of plateaulength to land length upon overall light output from the bottom of alight guide of the invention. FIG. 4 shows a magnified side view of aportion of an illuminated touch panel display generally identified as70. Structured light extraction layer 71 has projections such asprojection 72 bounded by riser 74, plateau 76 and facet 78, and flankedby lands 80 a and 80 b. The total length of all plateaus in layer 71 isless than the total length of all lands in layer 71, or in other wordsthe ratio of total plateau length to total land length is less than 1:1.Owing to the relatively small overall plateau area of layer 71, theavailable extraction window is relatively small and some of thepotentially reflective portion of buried facets such as facet 78 may beinaccessible to supplied light rays such as ray 46 a. Accordingly, asmaller fraction of such supplied light rays will be able to reach thefacets in layer 71 at a suitable angle so that the supplied rays can beextracted from light guide 12 through exit face 82, and the overalllight output from light guide 12 may be less than desired.

FIG. 5 shows a magnified side view of a portion of an illuminated touchpanel display generally identified as 90. Structured light extractionlayer 91 has projections such as projection 92 bounded by riser 94,plateau 96 and facet 98, and flanked by lands 100 a and 100 b. The totallength of all plateaus in layer 91 is greater than the total length ofall lands in layer 91, or in other words the ratio of total plateaulength to total land length is greater than 1:1. Owing to the relativelylarge plateau area of layer 91, most or all of the facet area isavailable for reflection, and supplied light rays such as ray 46 b willbe able to reflect from facets in layer 91 and be extracted from lightguide 12 through light exit face 99. Thus the overall light output fromthe bottom of light guide 12 in the illuminated touch panel of FIG. 5will tend to be greater than from the illuminated touch panel of FIG. 4.

FIG. 6 is a graph showing the relationship between the ratio of plateaulength to land length and light output from the exit face of the lightguide. In general, light output (or extraction efficiency) increases asthe ratio of plateau length to land length increases, in anapproximately logarithmic relationship. Preferably the ratio of totalplateau length to total land length is at least 1:1, more preferably atleast 3:1. Once the full facet is exposed and accessible to the suppliedlight rays, the plateau length diminishes in importance and the curveshown in FIG. 6 levels off. In general, it is preferred for the landlength to be greater than zero. For example, if the light extractionlayer is formed from a flexible film, then preferably the lands shouldnot be so short that it becomes difficult to peel away the film from theprofiled tooling that typically would be used to make a structuredflexible film.

FIG. 7 is a magnified partial side view of an illuminated touch panel100 of the invention, illustrating a potential source of light leakage.Some light rays such as ray 46 c will be reflected upward via totalinternal reflection from the lower face 102 of structured lightextraction layer 104 towards a buried facet such as facet 103. Atsufficiently low angles of incidence to the facet, light will refractedthrough the facet, pass through adhesive layer 105 and light guide 108,and exit the upper face 106 of light guide 108 at a high angle ofincidence, away from a typical user's view axis. This light will be lostand will not contribute to the viewer's perception of image brightness.

FIG. 8 is a magnified partial side view of an illuminated touch panel110 of the invention, illustrating a potential source of ghosting. Somelight rays such as ray 46 d will be reflected downward from a facet suchas buried facet 111, be reflected upward from the exit face 112 ofstructured light extraction layer 114, pass through adhesive layer 115and light guide 118, and exit the upper face 116 of light guide 118.These light rays will exit light guide 118 at a lower angle of incidencethan in the case of light ray 46 c in FIG. 7, and can be visible as aghost image of the illumination source.

FIG. 9 is a magnified partial side view showing an illuminated touchpanel 120 of the invention having a structured light extraction layer124 that can reduce light leakage such as is shown in FIG. 7, and anantireflection coating that can reduce ghosting of the type shown inFIG. 8. Light rays such as ray 46 e that are reflected upward from thelower face 122 of layer 124 are refracted through buried facet 126 andriser 128, and then are recaptured by refraction through nearby buriedfacet 130 and riser 132 back into layer 124. Light rays such as ray 46 fthat are reflected from a facet such as buried facet 126 strike thelower face 122 of layer 124 and pass through face 122 due to thepresence of antireflection coating 125 on face 122.

It is easier to apply a uniform antireflection coating to a flat surfacethan to a structured surface. Thus it is easier to employ such a coatingon the lowermost face (in other words, the light exit face) of theilluminated touch panels of the invention than on the lowermost face ofilluminated touch panels that employ refractive optics to extract lightthrough a structured surface on the lowermost face.

Those skilled in the art will appreciate that additional antireflectioncoating layers or other light management layers or features can beapplied to exit face 33, so long as care is taken preserve thesubstantially flat topography of exit face 33 and to avoid introductionof undesirable distortions in the viewed image.

Those skilled in the art will also appreciate that more than one lightsource can be used to supply light to the touch panel displays of theinvention. For example, referring again to FIG. 1, a plurality of lightsources can be placed along light input face 14. Although not shown inFIG. 1, a plurality of light sources could also be placed along end 15.If light is supplied along both input face 14 and end 15, then theprojections in the structured light extraction layer 32 (e.g.,projections such as projections 52 and 53 shown in FIG. 3) preferablyshould be symmetrically oriented with respect to the supplied light fromboth input face 14 and end 15. If light is supplied only along inputface 14, then end 15 is preferably equipped with a mirrored surface orother suitable reflector to direct light reaching end 15 back into lightguide 12.

FIG. 10 is a magnified partial side view of an illuminated touch panel140 having a light guide 142 and a structured extraction layer 144 thatcan reduce light loss. Light guide 142 is equipped with a specular ordiffuse reflector 146 that reflects light such as light ray 46 h backinto light guide 142. The amount of light reaching reflector 146 can befurther reduced by tilting or biasing the light source (not shown inFIG. 10), so that the axis along which the majority of its light outputfalls is not parallel to the upper face of light guide 142. Light rayssuch as light ray 46 g are reflected downwards from facets such asburied facet 148 and are extracted from layer 144. Light rays such aslight ray 46 h are reflected from reflector 146 back into layer 144 andreflected downward by reflection from facets such as buried facet 150,which is oppositely inclined from buried facet 148. These oppositelyinclined facets can be repeated along the length of light guide 142.

FIG. 11 is an exploded side view of an illuminated touch panel 160 ofthe invention, showing individual layers that can be assembled together.Touch-sensitive transducer layer 161 is formed on the upper face 164 oflight guide 162. Optically transparent adhesive layers 165 and 166 arecoated on opposite sides of carrier film 168, and set aside. Structuredlight extraction layer 170 is formed from base film 172 and alight-curable resin using a suitable profiled tool, then cured to formlight-cured structured surface 174 atop base film 172. If desired, anoptional antireflection coating (not shown in FIG. 11) can be applied tothe lower face of base film 172. This will be especially convenient whenstructured surface 174 is formed on base film 172 using a continuousmethod, as the antireflection coating can likewise be applied on thereverse side of base film 172 using a continuous method.

The plateau portions of structured light extraction layer 170 such asplateaus 180 a and 180 b are laminated to adhesive layer 166, takingcare not to damage the structured surface 174 of layer 170 and not tofill the air spaces between projections in layer 170 with adhesive.Adhesive layer 165 can then be laminated to the light output face 163 oflight guide 162. The resulting assembly can conveniently be sold as is,or combined with additional touch panel transducer or displaycomponents. For example, the assembly can be combined with the remainingcomponents of a capacitive overlay touch-sensitive transducer (not shownin FIG. 11) to provide a touch panel device that can be placed atop asuitable reflective light valve and equipped with a source of suppliedlight and suitable control electronics. As a further example, opticallytransparent adhesive layers 165 and 166 could be coated on oppositesides of carrier film 168, adhesive layer 166 could be laminated to theplateau portions of structured light extraction layer 170, and theresulting assembly sold as is for later lamination to the light outputface of a light guide.

If desired, a more complete assembly can be made by laminating polarizer176 to the upper face of reflective LCD 182 via adhesive layer 178.Reflective LCD 182 includes light modulation unit 184 and reflectivelayer 186. Other more complete or less complete assemblies can readilybe envisioned by those skilled in the art.

FIG. 12 is an exploded side view of another illuminated touch panel 190of the invention, showing individual layers that can be assembled andfastened to the light output face 193 of light guide 192.Touch-sensitive transducer layer 191 is formed on the upper face 194 oflight guide 192. Optically transparent adhesive layer 195 is applied tothe light output face 193 of light guide 192. Structured lightextraction layer 196 is formed from base film 198 and a light-curableresin using a suitable profiled tool, then cured to form light-curedstructured surface 200 atop base film 198. Structured layer 196 islaminated to adhesive layer 202 and polarizer 204, taking care not todamage the structured surface 200 of layer 196 and not to fill the airspaces between projections in layer 196 with adhesive. If desired, anoptional antireflection coating (not shown in FIG. 12) can be applied tothe lower face of base film 198. The assembly of FIG. 12 has fewerlayers and fewer optical interfaces in the light path than the assemblyof FIG. 11, but requires somewhat greater care in handling and duringlamination.

The light guide can have any desired overall size and thickness butpreferably it is as thin as possible, e.g., 5 mm or less. The lightguide can be square, rectangular, oval or any other desired shape whenviewed from the intended display observation point. The size and shapeof the light guide usually will be dictated by the size and shape of thedesired display device or desired touch panel. Light guide thicknessesfrom about 0.1 to about 5 mm are preferred, more preferably about 1 toabout 2 mm.

The light guide preferably is an optically suitable material capable ofresisting high temperatures and the steps required to fabricate atouch-sensitive surface atop the light guide. As mentioned above, thelight guide preferably is substantially planar. If planar, the lightguide can be fabricated from ordinary sheet glass. The light input faceand viewing face of the light guide can each be generally planar or canhave a convex or concave curvature. When the light source is a point orline source, the light input face may be provided with a convexcurvature, lenslets, prisms, a roughened surface or other features inorder to distribute the incoming light more evenly. The viewing facepreferably has an optically smooth finish, in order to minimizetransmission losses, undesired scattering and distortion.

The light extraction layer can be fabricated from a wide variety ofoptically suitable materials including polycarbonate; polyacrylates suchas polymethyl methacrylate; and polystyrene, with high refractive indexplastics such as polycarbonate being preferred. The light extractionlayer preferably is a flexible structured film made by molding,embossing, curing or otherwise forming a moldable resin against alathe-turned tool or other formed surface, made of metal or otherdurable material that bears a negative replica of the desired structuredsurface. Methods for making such formed surfaces and for molding,embossing or curing the extraction film will be familiar to thoseskilled in the art.

Individual light extraction layer designs can if desired be evaluatedwithout the need for actual layer fabrication, by using suitableray-tracing modeling software such as “ASAP” from Breault ResearchOrganization, Inc., “Code V” and “Light Tools” from Optical ResearchAssociates, “Optica” from Wolfram Research, Inc. and “ZEMAX” from FocusSoftware, Inc.

The facets that are present in the light extraction layer (and areburied in the assembled light guide and extraction layer) preferably aresufficiently small so as to be unobtrusive to an ordinary viewer. Theconfiguration, shape and dimensions of the facets and other lightmanagement features of the light extraction layer preferably are chosento maximize extraction efficiency and provide evenly distributed lightoutput at the desired viewing angle.

The projections preferably extend across the full width of the lightextraction layer. Although less preferred, the projections can be in theform of shorter, less than full width segments, which can be alignedwith one another in rows and columns or staggered from row to row. Rowsof projections can be arranged parallel to the light input face or facesor at an angle with respect to the light input face or faces. Mostpreferably, the projections extend across the full width of the lightextraction layer and are generally parallel to the light input face orfaces.

In the various embodiments of the invention shown in the Drawing,individual projections in the structured light extraction layers areshown as having the same angular orientation, shape and dimensions fromprojection to projection. The projections need not all be identical andneed not all have the same angular orientation, shape or dimensions. Forease of manufacturing, generally it will be preferred to form a lightextraction layer having projections whose riser, plateau and facetsegments have the same angular orientation and segment length fromprojection to projection. The land segments between such projections canif desired also be similar to one another in angular orientation andsegment lengths. Preferably however the projections are spaced at arelatively coarser pitch (repeat interval) near the light input face orfaces of the light guide, and at a relatively finer pitch further fromthe light input face. For a light guide illuminated from only one end,this change in spacing can conveniently be accomplished by progressivelydecreasing the length of the land segments along the length of the lightextraction layer from the light input face to the face at the other endof the light guide. A preferred pitch is from about 0.06 to about 12projections per mm at the light input face or faces to a maximum ofabout 250 to about 1 projection per mm further from the light input faceor faces.

Those skilled in the art will appreciate that formation of Moiré orother interference patterns can be discouraged or prevented in a varietyof ways. For example, the dimensions, angular orientation or spacing ofthe rows of projections can be adjusted relative to the dimensions,angular orientation or spacing of pixels or other repeating elements inthe reflective light valve (e.g., by skewing the direction of the rowsof projections a few degrees with respect to the direction of the rowsof pixels), so that interference patterns are minimized or eliminated atthe viewing face of the display.

Each light extraction layer riser segment preferably is planar althoughother shapes such as convex or concave shapes can be used if desired.Preferably the facets and other structured surface portions of the lightextraction layer are optically smooth, in order to avoid undesirablevisual artifacts that may arise due to backscattering of light withinthe light guide.

The light extraction layer preferably has a thickness of about 20micrometers to about 500 micrometers, more preferably about 75 to about125 micrometers. Facet heights (or in other words, land depths) of about5 to about 50 micrometers are preferred, more preferably about 7 toabout 20 micrometers. So long as the facets have sufficient height, thechosen extraction layer thickness has a relatively small effect onextraction efficiency.

Extraction efficiency tends to increase as facet heights increase, asthe light guide thickness is reduced, or as the projection pitchdecreases. That is, extraction efficiency tends to scale proportionallyto (facet height)/[(light guide thickness)*(pitch)]. Put slightlydifferently, extraction efficiency tends to scale proportionally to thetotal cross-sectional area of the facets divided by the totalcross-sectional area of the light guide input face.

The adhesive layers used to assemble the various layers in theilluminated touch panel displays of the invention can be pressuresensitive adhesives, adhesives cured using energy sources such as heat,UV or electron beam, or any other adhesive having acceptable optical andmechanical properties. Suitable adhesives and joining techniques will befamiliar to those skilled in the art. If desired, one or more of theadhesive layers can be cured after assembly, e.g., by applying theadhesive to one or both of the surfaces to be joined together, matingsuch surfaces together to form a laminated assembly, and exposing theadhesive layer or layers to suitable curing energy (e.g., UV or e-beam)through one or both sides of the laminated assembly to effect cure.

The adhesive layer between the light guide and the light extractionlayer should be applied with care. Such an adhesive can, for example, beapplied to the entire light output face of the light guide and the lightextraction layer laminated thereto. If desired, the adhesive can becoated atop only the plateau portions of the light extraction layer, andthe resulting partially-coated surface laminated to the light outputface of the light guide, e.g., as described in U.S. Pat. No. 5,545,280.In either case, appropriate care should be taken not to damage thestructured surface of the light extraction layer and not to fill thepockets between projections with adhesive.

If desired, the pockets between projections can be filled prior tolamination with a suitable flowable (and preferably hardenable) materialhaving a lower refractive index than the material from which the lightextraction layer is made. This can simplify lamination of the lightextraction layer to the light guide, and help discourage the adhesivefrom filling the pockets. However, if the flowable material has arefractive index between that of air and the material from which thelight extraction layer is made, then the use of such a flowable materialmay adversely affect the reflective characteristics of the facets andmay reduce overall extraction efficiency compared to the use ofair-filled pockets.

The illuminated touch panels of the invention are particularly useful insubminiature or miniature devices illuminated with one or more lightemitting diodes (LEDs) powered by small batteries. Suitable devicesinclude cell phones, pagers, personal digital assistants, clocks,watches, calculators, still and video cameras, laptop computers,vehicular displays and the like. The reflective light valves in suchdevices can be made using a variety of color or monochrome devices. Forexample, the reflective light valve can be a reflective color LCD suchas is used in the COMPAQ iPAQ™ Pocket PC. The reflective light valve canalso be a device capable of controlled frustration of total internalreflection such as the devices described in U.S. Pat. No. 6,064,784 andPCT Published Application No. WO 00/75720; a fixed graphic device suchas a poster or sign (e.g., a printed menu); or a variable-appearancesubstrate such as “Gyricon” electronic display material (underdevelopment by Gyricon Media Inc.). The illuminated touch panels of theinvention can be illuminated with more than one light source, e.g.,three or more LEDs. An array of colored light sources (e.g., one or moreof each of a red, green and blue LED) can be employed, with the lightsources in the array being electronically energized using a continuousor strobed addressing scheme. In addition to LEDs, other suitableillumination sources for the touch panels and displays of the inventioninclude fluorescent or incandescent lamps, electroluminescent lights andthe like. A particularly preferred light source for the touch panels ofthe invention employs the LINEAR ILLUMINATION SOURCE described incopending application Serial No. (attorney's docket no. 56209USA6A.002)filed on even date herewith, the disclosure of which is incorporatedherein by reference.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention. It should be understood that this invention is notlimited to the illustrative embodiments set forth above.

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 24. A flexiblefilm having a substantially flat lower surface and a non-planar uppersurface having finely-shaped projections with a generally trapezoidalcross-section comprising riser, plateau and facet portions flanked byland portions, wherein the facets have varied dimensions, pitch orangular orientation such that if the plateaus are laminated to the lightoutput face of a substantially planar light guide having at least onelight input face that supplies light to the guide, a viewing face andthe light output face opposite the viewing face, the facets will reflectand thereby extract supplied light from the guide through the light exitface and the supplied light will be evenly distributed across theviewing face.